1. Field of the Invention
The present invention relates to an optical writing device, an image forming apparatus, and a method of controlling the optical writing device, and in particular, to correcting degradation in image quality caused by fluctuation in interval between a photosensitive element and a light source.
2. Description of the Related Art
In recent years, there is a tendency to forward the computerization of information, and hence an image processing apparatus such as a printer or a facsimile used to output the computerized information, a scanner used to computerize documents, and the like is becoming an essential apparatus. Such image processing apparatus has an imaging function, an image forming function, a communication function and the like so as to be often configured as a multifunction peripheral (MFP) capable of being used as a printer, a facsimile, a scanner, and a copy machine.
An electrophotography image forming apparatus is being widely used for the image forming apparatus used to output the computerized document in such image processing apparatus. In such electrophotography image forming apparatus, an electrostatic latent image is formed by exposing the photosensitive element, such electrostatic latent image is developed using a developer such as a toner to form a toner image, and such toner image is transferred to a paper to carry out paper output.
In the electrophotography image forming apparatus, an optical writing device for exposing the photosensitive element includes a laser diode (LD) raster optical system type and a light emitting diode (LED) write type. An LED array (LEDA) head is arranged in the case of the LED write type.
In the LED write type optical writing device, the electrostatic latent image is formed by exposing a photosensitive element with the LEDA, as described above, but a spot diameter of a beam emitted from the LEDA and reaching the photosensitive element fluctuates if the distance between the LEDA and the photosensitive element fluctuates, and as a result, a density fluctuation in the image occurs.
For instance, if eccentricity occurs in the photosensitive element, if a film thickness differs according to the site on the surface of the photosensitive element, and the like, the distance between the photosensitive element and the LEDA fluctuates according to the rotation of the photosensitive element, and thus the density fluctuation occurs in a sub-scanning direction in the formed image.
In order to respond to such problem, a technique of maintaining the distance between the photosensitive element and the light source constant has been proposed (see e.g., Japanese Patent Application Laid-open No. 2010-008913, Japanese Patent Application Laid-open No. 2006-187929, and Japanese Patent Application Laid-open No. H7-052447). A technique for correcting the periodic fluctuation by the rotation of the photosensitive element has also been proposed (see e.g., Japanese Patent Application Laid-open No. 2007-144731).
When using the technique disclosed in Japanese Patent Application Laid-open No. 2010-008913, Japanese Patent Application Laid-open No. 2006-187929, and Japanese Patent Application Laid-open No. H7-052447, a component for maintaining the distance between the photosensitive element and the light source constant needs to be arranged, which complicates the component configuration, and increases the device cost and the management cost thus lowering productivity.
When using the technique disclosed in Japanese Patent Application Laid-open No. 2007-144731, the fluctuation in the image quality corresponding to the fluctuation in the relative speed with respect to the light source of the surface of the photosensitive element can be responded as the distance between the photosensitive element and the light source fluctuates.
However, the fluctuation in the image quality corresponding to the fluctuation in the beam spot diameter or the fluctuation in the beam intensity caused by the fluctuation in the distance between the surface of the photosensitive element and the light source cannot be responded by simply adjusting the light emitting cycle of the light source.
Therefore, there is a need for an optical writing device to prevent lowering in image quality caused by the fluctuation in the distance between the photosensitive element and the light source with a simple configuration.